Amber is a polymerized fossil resin derived from an extinct variety of pine. Although deposits of amber are to be found in several places throughout the earth, the most plentiful and widely employed source is found in the Baltic area, especially in what was known as Prussia, more especially in and around the cities of Danzig and K onigsberg. Amber resin can be from a pale yellow to a reddish-brown colored resin which softens at about 150.degree. C. (302.degree. F.) and has a melting point of about 350.degree. to 375.degree. C. (662.degree. to 707.degree. F.). From very ancient times amber has been added to drying oils to prepare varnishes. The addition of amber to drying oils increases the drying rate and the glass transition temperature, Tg, of solvent free drying oils so that film hardness is achieved more rapidly.
With the flowering of oil painting in the 16th and 17th centuries, especially in the Flemish school by Van Eck, Memling and others and in the Italian school by Perugino, Da Vinci, Bellini, Correggio and others, the superior qualities of amber-based varnish was recognized especially as a vehicle for pigments. The use of amber-linseed oil varnishes, generally manufactured by the artists themselves during this period, provided an especially suitable medium for the union of various colors and tints--enabling the artists to imitate nature in their paintings. Anyone who has viewed paintings by the artists of this era recognizes this quality in their paintings. However, with the passing-on of these artists the manufacture itself of such high quality amber-based varnishes disappeared and production of amber-based varnishes became problematic since the methods devised for producing same resulted in amber varnishes having undesirable color characteristics of darkness and lack of clarity.
One of the problems with amber-based varnishes is that, although they possess superior qualities of durability, smoothness and hardness among others, it has not been considered possible to produce such varnishes in a colorless condition and with a transparency such that when mixed with pigments, especially white and blue pigments, so as to avoid some undesirable yellowing of the pigments or loss of brilliance, lustrousness or clarity of the pigments.
Over the last several centuries, although some art historians have believed that the amber-based varnish manufacturing methods of the 16th and 17th centuries artisans has been "lost" because it has not been possible to produce sufficient colorless amber-based varnish to avoid the yellowing problem with white and blue pigments, other art historians have questioned whether or not said artisans actually were able to employ such amber-based varnishes as pigment mediums and have postulated all manners of theories as to what those ancient artisans might have employed instead of amber-based varnishes in order to retain the brilliance, luster and clarity of such pigments in their paintings.
Since it has not been possible to produce such clear, essentially colorless amber-based varnishes, the use of amber in varnishes has been replaced by other natural resinous materials such as copal, rosin, congo gum, dammar and the like and by synthetic resins such as phenol-formaldehyde or urea-formaldehyde resins. However, varnishes based on these other resins, both natural and synthetic, lack the superior qualities of amber-based varnishes and do not enable artisans to obtain the satisfactory union of colors and tints with the desired durability, smoothness and hardness to enable them to imitate nature in their paintings in the manner achieved by the 16th and 17th century artisans.
It is therefore highly desirable that amber-based varnishes having sufficient characteristics of colorness and clarity be available to artisans so that said artisans can employ those varnishes as vehicles for all pigments, but especially white and blue pigments, without loss of brilliance, luster and clarity and permitting the artists to produce pictures imitating nature, and allowing for satisfactory union of colors and tints to produce almost any gradation considered desirable. It is further desirable that a method for producing such essentially clear, colorless amber-based varnishes be available. Such varnishes can also be used as varnishes for woodworking and for varnishing musical instruments and the like or for any use calling for application of a varnish.